I wish there were some fun way to explain why urine is yellow. Unfortunately, the answer is kind of boring and all scientific. Some scientists in the middle-ages, called alchemists, were obsessed with producing gold from other substances. Some of these alchemists believed urine was yellow due to the presence of gold. Try as they might, however, the alchemists were never able to extract gold from their own pee.

Today, we know that the yellow color of urine is not from gold, but from chemicals called urobilins. Urobilins come from bilrubin, and bilrubin is made from old red blood cells. Bilrubin is found in quantities in the bile. It gives bile its color, and it is partially responsible for the brown color of feces. Bilrubin begins in the circulatory system but is extracted from the blood by the liver. The liver sends bilrubin to the gall bladder where it is deposited into the intestines. The liver is unable to gather all the bilrubin, so some of it gets into the kidneys as waste liquids are being removed from the system. In the kidneys, the bilrubin is broken down into urobilin, also called urochrome. The more water someone has in their system, the urochrome will be less concentrated, so the urine is less yellow. When someone has less water in their system, the urochrome is more highly concentrated, so the urine is more yellow.

Some foods and vitamins can also cause urine to yellow, orange, or even green. Eating excessive amounts of beets and carrots can turn urine orange. A diet high in asparagus can give urine a green tint. High amounts of vitamin B and C can turn urine a bright yellow.